Explain why farmers use selective breeding to produce new varieties of wheat with higher grain yields, and describe one disadvantage of this process.

AQA GCSE Biology (8461) — 4.6.2 Variation and evolution · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Farmers have used selective breeding for thousands of years to improve crop plants. Modern wheat varieties produce far more grain per plant than wild wheat ancestors.

Model answer (4 marks)

Farmers select the plants that give the highest grain yield and breed them together. Repeating this over many generations ensures that the offspring inherit the alleles that cause high yield. A disadvantage is that the process reduces genetic variation in the wheat population, making it more vulnerable to disease or environmental change because few or no individuals carry resistant alleles.

Examiner tips

Use the word ‘select’ and ‘breed’ to show the process; mention inheritance of alleles; state the disadvantage and its consequence; keep answer concise to fit 4 marks.
Include the link between reduced variation and vulnerability to disease to demonstrate full understanding.

Common mistakes

Confusing selective breeding with random mutation; not mentioning inheritance of alleles; omitting the link between reduced variation and disease vulnerability.

Mark scheme (4 marks)

Farmers choose/select plants with the highest grain yield (desirable characteristic) and breed them together
This is repeated over many generations so that offspring inherit the alleles for high yield
A disadvantage is that it reduces genetic variation in the population (inbreeding)
This means the population is more vulnerable to a new disease or change in environment (because few/no individuals carry resistant alleles)

Key terms in this question

selective breeding